Method for forging particles



Unite States This invention relates generally to hot die forging, and more specifically to fa technique for forging powder and particulate fabricated blanks.

In die forging, cast or wrought blanks are formed into metallic shapes by placing the blank between a pair of dies which have the desired impression of the finished forging shape, and subjecting the assembly to repeated blows. The drop forging hammer contains a ram which carries a die operating in the vertical plane and an anvil block in which the stationary die is keyed. The two dies are matched together so that the impressions therein are in alignment, whereby the forging impact causes the metal to fill the cavities for the production of the prescribed design. The means by which the ram is operated determines the nomenclature of the hammer. Among the hammers in use are steam and air drop hammers as well as board drop and helve hammers. Also in use in place of hammers are presses which are hydraulically operated to subject the die to for-ming pressure. Forgings are ordinarily made from cast billets sheared or sawed to the individual lengths required for the production of a single piece.

Accordingly, it is the main object of this invention to provide preformed blanks for hot forging, constituted by powder-fabricated bodies rather than cast or wrought billets heretofore used, thereby effecting a substantial reduction in forging costs. Such cost reductions are effected for the following reasons:

(A) The powder-fabricated forging blanks are prepared from low-cost starting materials which are readily preformed for forging.

(B) The powder-fabricated blank conforms generally to the ultimate shape of the finished part; hence less ash is produced and less material losses are incurred during forging.

(C) Since the powder-fabricated blank is preformed and highly porous, it is more easily forged, requiring fewer forging blows in the case of hammer forgings and lesser presures in the case of press forgings.

Also an object of the invention is to provide blanks for hot forging, which blanks 'are constituted by loose powders contained within a foil envelope, or blanks formed by cold-pressing powders into preforms.

Briefly stated, these objects are accomplished by introducing between the matching dies of a forging mechanism heated metal particulates which may either be loose, contained in a foil envelope of the same metal or cold-compacted to provide a preformed blank, and subjecting the particulates to forging pressures to produce a consolidated part having a shape determined by the die impressions.

For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description of the invention to be read in conjunction with the accompanying drawing, wherein:

FIGURE l is a schematic diagram of a forging arrangement in accordance with the invention; and

FIGURE 2 is a graph showing the mechanical properties of forgings made in accordance with the inventive process.

The invention wi-ll be :described in connection with aluminous particulates, but it will be appreciated that the process is applicable to a wide variety of starting meterials.

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It has been found that the materials most easily and effectively forged are relatively coarse particulates such as centrifugally spun needles ranging in size from -20/-1-80 to +200 mesh. Either pure aluminum or prealloyed particulates in a variety of common alloy compositions, such as types 2024, 7075, etc., may readily be processed. The process is not limited, however, to the use of any type, size or shape of particles.

Direct hot forging of the selected powders is accomplished in either of two ways:

(1) By preheating the powders to be forged, depositing them in a confining die constituted by upper and lower elements 10 and 11, as shown in FIG. 1, and impacting or statically pressing them to the desired shape. If need be, more than one die may be used in producing the finished part, the first die being used to convert the powders to a coherent mass (blocking) and the remaining dies being used to forge the part to its final shape.

(2) By packaging the loose powders in aluminum foil, the package having the general shape required of the finished forging. In this case, the packaged powders have enough rigidity to be preheated, transferred to the forging die and forged in much the same way as in a conventional forging blank. In the case of the packaged powder forging blank, however, fewer and less severe forming operations are required because of the high voidage of the package and its preformed shape.

The preheat temperatures used for the loose powder of powder package preforms, depends upon their composition, but in the case of aluminous powder the range is preferably 400 C. to 600 C. The higher temperatures are generally used for pure aluminum or slightly alloyed aluminum, -and the lower temperatures for heavily alloyed aluminum. The pressures needed for forging will depend on the size of the part processed and its complexity. In the case of a relatively simple part with a cross-sectional area of 6% square inches, five blows with a BOO-pound forging hammer, using a two-foot drop, results in a satisfactorily forged part.

The properties of solution-treated and artificially aged forgings prepared from aluminum foil-packaged, type 2024 aluminum alloy needles, are shown in FIG. 2. Note that mechanical properties of the forgings improve -as the depth of the die cavity in which the preforms are initially forged decreases, indicating that when forging powders it is desirable to use high reductions during the initial stages of forging. Note too, that there is an optimum forging temperature, which in the case of this alloy, corresponds to about 600 C.

In the above examples, either loose particulates are hot forged in a closed forging die, or the particulates are placed within a foil envelope to be forged. It is also possible to hot forge blanks prepared from cold-pressed aluminum or aluminum alloy particulates.

In the case of certain metal particulates, for example, aluminum and aluminum alloy needles, the forging can be started at lbetween the solidus and liquidus temperatures in presence of a liquid phase. The presence of some liquid phase aids consolidation and bonding and, reduces by as much as 1/2 the number of forging blows required. In contrast, conventional cast-wrought blanks cannot be forged in the presence of a liquid phase. -Forging blows in the presence of a liquid, would tear the cast-wrought metal apart into several pieces or result in a part with numerous cracks.

The following example is illustrative of the subject forging technique as applied to the fabrication of an unalloyed aluminum forging. Aluminum particulates consisting of needle-shaped particles approximately 20/60 -mesh size, having a length-to-diameter ratio of 3 or more, are mixed with 1A to 1 weight percent solid lubricant. The particulates are deposited in a dies cavity measuring 11A" X 3% X 11/2 deep, pressed at 5 to 20 t.s.i., or at any convenient pressure which results in a compact which withstands the necessary subsequent handling operations. The compact density after cold-pressing may vary from slightly higher than bulk density to 100% of theoretical. The compact is then preheated at 400 C to 600 C. in air or an inert atmosphere until thermal equilibrium is reached, and then hot forged in one one or more blows with a drop hammer or other type of forging press.

The forging conditions and mechanical properties obtained from high and low density green compacts are given in Table I below. Note that the data is for compacts prepared from pure aluminum particulates, but that the process may, through use of prealloyed particulates, be readily adapted to the fabrication of aluminum alloy forgings in a wide variety of commercial compositions, e.g., types 20:24, 7075, etc. It is again stressed that the process is not limited to the use of particulates of any specific size, any of a variety of particle sizes greater than powder size being processed with equal facility.

TABLE L FABRICATION CONDITIONS AND MECHANICAL PROPERTIES OF FORGINGS PREPARED FROM COLD PRESSED ALUMINUM PARTICULATES Sample Number F-lQG F-197 Initial Density, Percent Theoretical-" 75 98 Hammer Weight, Pounds 300 300 Hammer Drop, Inches 25% 25% Size, Inches, Height x Width x Length. 1.035 X 1. 250 X 1. 260 X 0. 890 x 3. 325 3. 325 Preheat Temperature, C 600 600 Total Number of Forging Blows 5 6 Total Reduction in Height, Percent of Initial Height 36. 3 25.0 Ultimate Tensile Strengt as annealed, p.s.i 11, 290 10, 340 Elongation, Percent as annealed 44 42 Hardness, Rockwell H, as annealed- 44 51 It should be understood that this method is also applicable to the use of not only particu-lates above powder size, but powders as well (below 1000 microns). In fact, the method is so versatile that any type of aluminum particulate, even scrap turnings, so long as it can be green-compacted into a handleable compact, can be heated and directily forged.

While there has been shown a preferred embodiment of the invention in hot forging of particulate blanks 4- described above, it will be appreciated that many changes and modiiications may be made therein without, however, departing from the essential spirit of the invention as dened in the annexed claims.

What is claimed is:

1. The method of die forging, comprising the steps of introducing heated metal particulates contained in a foil envelope between the matching dies of ya forging mechanism, the assembly being heated above the temperature where incipient fusion of said metal particulate begins but below the temperature of complete melting, and subjecting the particulates in the dies to forging pressures to produce a consolidated part having a shape determined by the die impressions.

2. The method of die forging, comprising the steps of heating aluminous particulates contained in a foil envelope to a temperature in the range of 400 C. to 600 C., introducing `said heated particulates contained in a foil envelope between the matching dies of a forging mechanism, and subjecting the particulates in the dies to forging pressures to produce a consolidated part having a shape determined by the die impressions.

3. The method as set forth in claim 2, wherein said particulates are relatively coarse and range in size from -20/-l-80 mesh to 80/+200 mesh. v

4. The method of die forging, comprising the steps of heating aluminous particulates contained in a foil envelope to a temperature above the point at which incipient fusion begins but below the point at which the metal becomes completely molten, introducing said heated particulates contained in a foil envelope between the matching dies of a forging mechanism, and subjecting the particulates in the dies to forging pressures to produce a consolidated part having a shape determined by the die impressions.

References Cited by the Examiner UNITED STATES PATENTS 2,275,592 3/ 1942 Menihan. 2,749,604 6/1956 Latin 29-420-5 3,144,330 8/1964 Storchheim. 3,146,099 8/1964 Teja 29-4205 TOHN F. CAMPBELL, Primary Examiner. P. M. COHEN, Assistant Examiner. 

1. THE METHOD OF DIE FORGING, COMPRISING THE STEPS OF INTRODUCING HEATED METAL PARTICULATES CONTAINED IN A FOIL ENVELOPE BETWEEN THE MATCHING DIES OF A FORGING MECHANISM, THE ASSEMBLY BEING HEATED ABOVE THE TEMPERATURE WHERE INCIPIENT FUSION OF SAID METAL PARTICULATE BEGINS BUT BELOW THE TEMPERATURE OF COMPLETE MELTING, AND SUBJECTING THE PARTICULATES IN THE DIES TO FORGING PRESSURES TO PRODUCE A CONSOLIDATED PART HAVING A SHAPE DETERMINED BY THE DIE IMPRESSIONS.
 2. THE METHOD OF DIE FORGING, COMPRISING THE STEPS OF HEATING ALUMINOUS PARTICULATES CONTAINED IN A FOIL ENVELOPE TO A TEMPERATURE IN THE RANGE OF 400*C. TO 600*C., INTRODUCING SAID HEATED PARTICULATES CONTAINED IN A FOIL ENVELOPE BETWEEN THE MATCHING DIES OF A FORGING MECHANISUM, AND SUBJECTING THE PARTICULATES IN THE DIES TO FORGING PRESSURES TO PRODUCE A CONSOLIDATED PART HAVING A SHAPE DETERMINED BY THE DIE IMPRESSIONS. 